The present invention relates to addition compounds of their salts suitable for use as dispersing agents and as dispersion stabilizers, obtainable by reaction of polyisocyanates, hydroxy compounds and compounds containing Zerewitinoff hydrogen as well as at least one acidic functional group, hydroxy group or alkoxysilyl group, optionally in the presence of solvents and optionally in the presence of reaction catalysts.
The invention further relates to a process for producing these addition compounds, to their use as dispersing agents and dispersion stabilizers, and to powdered or fibrous solids which are to be worked into liquid systems and which are coated with such dispersing agents.
In order to introduce solids into liquid media, high mechanical forces are required. To reduce these dispersion forces, it is conventional to utilize dispersing agents which make it easier to work the solids into the liquid. In general, these are surface active materials, also called tensides, having anionic, cationic as well as non-ionic structures. These materials are used in small amounts, either applied directly to the solids or added to the dispersing medium. By using such a tenside, the dispersion energy is substantially reduced.
It is further known that these solids tend to reagglomerate after the dispersion process due to mutual attraction forces, which nullify the previously expended dispersion energy and lead to serious problems.
An inadequate dispersion becomes apparent through a viscosity increase in liquid systems, total loss of color distinctions in lacquers and coatings, insufficient color development in pigmented synthetic plastics, and decreases in the mechanical strength of reinforced synthetic plastics.
Dispersing agents have been suggested to solve this problem, for example in U.S. Pat. No. 3,788,996; U.S. Pat. No. 3,817,944; U.S. Pat. No. 4,029,861; U.S. Pat. No. 4,032,698; U.S. Pat. No. 4,048,207; U.S. Pat. No. 4,070,388; DE No. 2,125,064, EP No. 0.018,099; EP No. 0,127,325; FR No. 2,241,597; GB No. 1 339,930; GB No. 1 393,401 and GB No. 1 393,402. However, these dispersing agents lead only to partial solutions of the problem, particularly with regard to flocculation-free mixability of various pigments with each other, such as organic pigments and inorganic pigments. Pigment pastes produced according to the aforedescribed process also tend to undergo exchange effects with the surrounding medium, for example after inclusion in lacquers. It can thereby be concluded that the adsorbtion layers which are built up, do not exhibit sufficient stability against desorption.
According to the latest state of the art described in European Patent Application No. 0,154,678, the aforementioned disadvantages can be substantially overcome by use of the addition compounds proposed therein. With these addition compounds outstanding results can be achieved in part. However, a positive effect cannot be generally achieved with all solids to be dispersed and all binders. In a whole series of cases the results achieved are not sufficient to form an absorbtion layer which is stable for a longer period of time and thus assure a sufficient stability.
In addition, in every instance the addition compounds according to EP No. 0,154,678 contain basic nitrogen atoms. As is well known to persons skilled in the art, such basic groups can be disadvantageous in certain fields of application in which such groups lead to exchange effects with the surrounding medium, such as, for example, a decrease in the storage stability of two-component polyurethane systems due to a reaction accelerating effect or accelerating the polymeric decomposition of polyvinyl chloride under thermal stress.